A suspension of 2B —which contained approximately 50% of methyl 5-(4-chlorophenyl)-1,3,4-oxadiazole-2-carboxylate as an impurity—(1.38 g, 2.47 mmol) in dichloromethane (50 mL) was cooled in an ice-bath. Triethylamine (0.51 mL, 3.70 mmol) was added followed by methanesulfonyl chloride (0.27 mL, 3.45 mmol). After the addition, the cooling bath was removed. The mixture was stirred for 7 h. The reaction mixture was transferred to a reparatory funnel and was washed with water followed by aqueous NaHCO3. The organic solution was dried (phase separator) and evaporated. Dichloromethane (50 mL) and diethyl ether (200 mL) were added and the solid product was collected by filtration. The solid was washed twice with diethyl ether and then dried in vacuo. The product was purified using flash column chromatography first eluting with dichloromethane and then with a mixture of dichloromethane and methanol containing 2M NH3 (20:1). There was obtained 0.66 g (75%) of 2C as a solid. 1H NMR (500 MHz, CDCl3): δ 3.13 (s, 3H), 4.43 (dd, 1H), 4.65 (dd, 1H), 4.87 (dd, 1H), 5.12 (dd, 1H), 5.41 (m, 1H), 7.53 (d, 2H), 8.10 (d, 2H), MS (APCI+) m/z 358 [M+H]+.
